The present invention relates to a thermal process gas-flow measuring apparatus and method used for detecting the condition of, for example, an engine fuel injection control apparatus by measuring the amount of intake gas supplied to the engine.
In a conventional electronic fuel injection control apparatus for a vehicular engine, data regarding the condition of the engine such as its rpm or the amount of intake gas is detected and measured. The basic amount of fuel injected for every revolution of the engine is calculated in accordance with the detection/measurement signal. This basic amount is corrected in accordance with parameter data such as data about the temperature of the cooling water for the engine. Thus, the final amount of fuel injection is calculated to control a fuel injection valve.
In general, the fuel injection valve receives fuel at a predetermined pressure. The valve comprises an electromagnetic injection valve whose amount of fuel injection is determined when the valve is on. Therefore, the fuel injection data comprises a signal for designating when the electromagnetic injection valve is on. The on signal is synchronized with the revolution of the engine so as to control the injection of the fuel.
This conventional fuel injection control apparatus for an engine generally employs a low loss, highly precise, thermal process, gas-flow measuring apparatus capable of measuring the amount of gas flow over a wide range.
Typical examples of a conventional fuel injection control apparatus of this type are described in U.S. Pat. Nos. 4,384,484, 4,393,702 and 4,399,697. Each of these conventional fuel injection control apparatuses comprises a heater supplied with a heating current and having a temperature-resistance characteristic, and a resistive element which receives heat from the heater, the element also having a temperature-resistance characteristic. The heater and the resistive element are arranged in an intake pipe. The temperatures of the heater and the resistive element are read from the resistances thereof, and the heat radiation conditions of the heater and the resistive element which are influenced by a gas flow are also measured. A signal corresponding to the measured amount of gas flow is generated.
However, in such a thermal process gas measuring apparatus, the heater must be at a higher temperature than the ambient temperature when a heating current is flowing through it. Immediately after the heating current begins to flow in the heater, the temperature of the heater is not at the necessary heated state. Until the heater attains thermal equilibrium, an output signal is generated from the heater independently of the amount of gas flow.
The heater and the resistive element which constitute the measuring apparatus are wound around a heat-resistant frame to provide good mechanical strength. The frame must also attain thermal equilibrium so as to cause the measuring apparatus to operate normally. The frame temperature is the same as that of gas under normal circumstances. When the heating current is supplied to the heater, the frame must also be heated to the same temperature as that of the heater. Since the frame temperature is the same as that of the normal gas, the heater and the frame are heated to the same prescribed temperature. Therefore, initially, when the heating current flows through the heater, the output signal erroneously indicates that the amount of gas flow is larger than it actually is.
When such an erroneous output signal from the gas-flow measuring apparatus is supplied to the fuel injection control apparatus which calculates the injection quantity, the air/fuel ratio may become excessive immediately after the engine is started. As a result, ignition efficiency is degraded, the emission level is decreased, and drivability after the engine is started becomes impaired.